1. Field of the Invention
The present invention relates to a rubber composition having a specific furnace carbon black incorporated therein. More particularly, the invention relates to a tire tread rubber composition capable of providing a tire tread having small energy loss and a great coefficient (.mu.w) of sliding friction on a wet road surface.
2. Description of the Prior Art
With the current worldwide concern for saving resources and energy, car manufacturers are making intensive efforts to manufacture automobiles which achieve better mileage economy. To meet this end, studies have been conducted by tire manufacturers to find effective ways to minimize energy loss through tires.
Two principal functions of tires are to support the weight of the automobile and to transmit the driving force of the wheels. As is well known, the energy loss resulting from the friction between a tire and the road surface or from the heat generated by the tire itself has an appreciable effect on the fuel consumption of the car. However, the energy loss which results from the tire itself, i.e., its rolling resistance, cannot be reduced without also decreasing the coefficient (.mu.w) of its sliding friction against a wet road surface. In other words, a tire with a small rolling resistance has a great tendency to skid.
In order to attempt to resolve these contradictory factors, studies have been conducted which involve the incorporation of carbon black in large quantities into rubber to prepare a tire tread rubber composition which has a small rolling resistance while exhibiting a high coeffficient (.mu.w) of sliding friction on a wet road surface.
It is generally known that the rolling resistance (RR) of a tire is a function of E"/E'=tan .delta., wherein E" is the loss elastic modulus and E' is the storage elastic modulus. Tires having a low loss tangent (tan .delta.) also have a low rolling resistance (RR). The coefficient (.mu.w) of sliding friction on a wet road surface is also closely related to the viscoelasticity property of rubber and, the higher the tan .delta., the higher the .mu.w. However, a rubber composition having a high tan .delta. has an undesirably high rolling resistance (RR).